Engine fuel systems are known which include a fuel distribution valve assembly having a single fuel inlet port and multiple fuel discharge ports. An individual fuel manifold conduit separately supplies fuel from each of the discharge ports to a fuel injector assembly such as a fuel nozzle having an inlet port and a spray tip outlet for injecting fuel into the engine combustor whether a variable volume cylinder or a fixed volume chamber.
In order to produce controlled fuel distribution throughout the system, heretofore the fuel flow versus fuel pressure characteristics of each component of the system is determined. Desirably, these characteristics are held within a range so that components of the system can be interchanged by like components without affecting the controlled distribution of system fuel flow. However, each system component and replacement parts for each component have slightly different fuel flow versus fuel pressure characteristics. In order to calibrate the system for interchangeability of injector parts, normal practice has been to place a trimming orifice in the inlet of each fuel injector. This orifice is removable and size adjustable to adjust the fuel flow versus fuel pressure from the inlet of the distribution valve to the spray tip of each nozzle. All of the injectors in the system can be held to close flow limits by use of such trim orifices which can be located in the inlet of the injector.
The same procedure has been used to adjust individual fuel injectors to have closely held flow limits for interchangeability. In such cases the trimming orifice is normally located in the inlet end of the manifold assembly to provide manifolds with like fuel flow versus pressure characteristics.
Because of dimensional variations in the system, each individual fuel manifold can have varying lengths and shape (bends, turns and the like) between its connection to the outlet of the distributor valve and its connection to the inlet of the fuel injector. In such cases it can be impractical to hold all manifolds to the same characteristics. In such cases, manifolds of a given length and shape are held to close flow limits by use of trimming orifices to provide interchangeability of such manifolds without affecting total system distribution.
The fuel distribution valve in such systems desirably has identical fuel metering slots or holes for distributing metered fuel to each system manifold and injector. Such slots or holes are easier to manufacture, however, they require some form of flow adjustment downstream of the metering to adjust for valve inequalities such as internal valve manifolding of variable length, size or shape or like differences in internal valve passages because of manufacturing variations. To accurately test fuel distribution from the distribution valve assembly it is necessary to direct fuel through the complete system or its analog to take into account intersystem cross-leakage.
Fuel flow versus fuel pressure variations within the valve are presently adjusted by use of replaceable trimming orifices like those used in association with each manifold and each nozzle. Adjustment of fuel characteristic variations within the valve is more difficult when total system flow occurs, since adjustments made in one of the internal valve passages with affect distribution through the other internal valve passages. As a result, testing and adjusting of distribution valves is a long, tedious procedure that requires system shut-down and repetitive assembly and trial and error replacement of trimming orifices in the system components before a fuel distribution valve is trimmed for use in a fuel supply system.